SELECT        T1.IDCUST, T1.IDINVC, T2.AMTPAYM, 'SumofRows' AS TotalPayment
FROM            MyTable1_ARIBH T1 INNER JOIN
                         MyTable2_ARTCP T2 ON T1.IDCUST = T2.IDCUST AND 
                         T1.IDINVC = T2.IDINVC
WHERE        (T1.IDCUST = 'TOR829') AND (T1.IDINVC = '72124')

SELECT        
	T1.IDCUST, 
	T1.IDINVC, 
	T2.AMTPAYM, 
	Dev1.TotalPayment
FROM            
	MyTable1_ARIBH T1 
INNER JOIN
	MyTable2_ARTCP T2 
	ON 
		T1.IDCUST = T2.IDCUST 
		AND 
        T1.IDINVC = T2.IDINVC
INNER JOIN
	(
	SELECT        
		T1.IDCUST, 
		T1.IDINVC, 
		SUM(T2.AMTPAYM) AS TotalPayment
	FROM
		MyTable1_ARIBH T1 
	INNER JOIN
		MyTable2_ARTCP T2 
		ON 
			T1.IDCUST = T2.IDCUST 
			AND 
            T1.IDINVC = T2.IDINVC
	WHERE
		T1.IDCUST = 'TOR829'
		AND
		T1.IDINVC = '72124'
	GROUP BY 
		T1.IDCUST, 
		T1.IDINVC
) AS Dev1
	ON 
		T1.IDCUST = Dev1.IDCUST
		AND 
		T1.IDINVC = Dev1.IDINVC
WHERE
	T1.IDCUST = 'TOR829'
	AND
	T1.IDINVC = '72124'

SELECT
	T1.IDCUST, 
	T1.IDINVC, 
	T2.AMTPAYM, 
	TotalPayment = SUM(AMTPAYM) OVER (PARTITION BY IDCUST, IDINVC)
FROM MyTable1_ARIBH T1 
INNER JOIN MyTable2_ARTCP T2 
	ON T2.IDCUST = T1.IDCUST  
	AND T2.IDINVC = T1.IDINVC 
WHERE T1.IDCUST = 'TOR829' 
	AND T1.IDINVC = '72124'